Working with already-exploded EPUBs in v3

[smoores-dev]

It seems like the kotlin v3 toolkit no longer has built in support for treating an already-extracted zip directory as an EPUB asset. This was an option in v2 — you could pass a directory path to the streamer, and it would treat the directory like an unzipped archive.

In Storyteller, I've been storing EPUBs on device extracted into directories. This is because:

• These EPUBs are often very large, which means that unzipping them can be fairly expensive/slow, so it's nice to just do it once
• Until Readium supports Media Overlays/Guided Navigation, I need to do the audio management myself, so I need the unzipped audio files from the EPUB, anyway

What would be the best way to handle this? Should I write an ArchiveOpener that operates on extracted folders?

[mickael-menu]

We changed this in v3 because we do not recommend using exploded archives for implementers. For your use case, you should be able to access the content of the audio files once the Publication object is opened by using publication.get() and the Resource API. However, I understand that this may not work if you depend on a third-party library for processing the audio files, which requires having the files on disk instead of accessing the bytes in memory.

It is in fact still possible to open exploded EPUBs in v3, just not as obvious.

ArchiveOpener will not help you because it is meant to open a file (archive) as a Container of Resource objects instead of a single Resource.

Instead, you can directly create a DirectoryContainer if you know that the publication is exploded as a directory. Then, use this AssetRetriever API with the Container to get an Asset as usual.

[smoores-dev]

However, I understand that this may not work if you depend on a third-party library for processing the audio files, which requires having the files on disk instead of accessing the bytes in memory.

Yup, this is exactly the issue.

As always, thanks so much for the response, @mickael-menu! This is exactly what I was looking for